Apparatus and method for igniting sample in calorimeters

ABSTRACT

Apparatus for igniting a sample in a calorimeter. A heating element is used to ignite a solid or liquid substance, inside the calorimeter, and the burning substance is allowed to move onto a sample in a crucible to ignite the sample.

BACKGROUND OF THE INVENTION

[0001] This invention is concerned generally with a calorimeter and moreparticularly is concerned with the ignition of a sample in acalorimeter.

[0002] A sample material which is to be tested in a calorimeter isnormally ignited using one of two methods.

[0003] In the first instance use is made of a length of resistance orfuse wire which is positioned so that it contacts a sample materialwhich is in a calorimeter and which is to be ignited. An electriccurrent is passed through the wire which is thereby heated to atemperature which causes ignition of the sample material. Although thistechnique works satisfactorily the resistance wire has a short life timeand, in some applications, must be replaced after the combustion of eachsample material.

[0004] It is also known to make use of a combustible thread such ascotton which is brought into contact with, or positioned so that itextends into, the sample material. A portion of the thread is attachedto a resistance or fuse wire which is heated by passing an electricalcurrent through the wire. When the temperature of the wire is increasedsufficiently the thread is ignited and burns along its length and theflame ignites the sample material once the flame reaches the samplematerial. Again this process works satisfactorily but it suffers fromthe drawback that a correctly positioned fresh thread must be insertedinto the calorimeter each time a sample is to be ignited.

[0005] Many calorimeters have been automated so that practically all therequired steps in a calorimetric measurement are automatically carriedout in the correct sequence. The problem associated with igniting thesample material, ie. the repeated replacement of the resistance wire orcombustible thread, as the case may be, has however mitigated againstthe implementation of a completely automated process.

SUMMARY OF THE INVENTION

[0006] The invention provides apparatus for igniting a sample in acalorimeter which includes a heating device, holder means for placing acombustible substance in contact with or in proximity to the heatingdevice thereby to ignite the substance which, once burnt to apredetermined extent, is movable away from the heating device, and asample holder which is positioned to receive the burning substance as itmoves away from the heating device.

[0007] The sample holder may be of any appropriate type and preferablyis a conventional crucible.

[0008] The burning substance may be movable away from the heating devicein any appropriate way and preferably is movable under gravity actionor, at least initially, under the action of pressure which is generatedby the burning substance. In this instance the sample holder, ie. thecrucible, is positioned lower than the heating device and is orientatedso that a sample on the sample holder will be impacted by the movingburning substance.

[0009] The heating device is preferably electrically operated. Theheating device may take on any suitable form and for example may includeor comprise a filament wire, a resistance wire, or any equivalent devicewhich is heated by the passage of electric current at least to atemperature which is equal to the ignition temperature of the substance.

[0010] The holder means may be part of or be formed by the heatingdevice. For example in one form of the invention the heating deviceincludes at least one filament wire shaped to receive the combustiblesubstance. The filament wire may have a loop which is in proximity to,or which receives, the combustible substance and, as the combustiblesubstance is burned, its size diminishes to a point at which thecombustible substance is automatically disengaged from the loop. This isgiven merely by way of a non-limiting example.

[0011] In a preferred form of the invention the holder means is afunnel-shaped component in which the combustible substance is locatedand the heating device is positioned inside the funnel so that thecombustible sample, inside the funnel, is automatically brought intocontact with, or in proximity to, the heating device.

[0012] The funnel may include an outlet which is located above thesample holder with the outlet being sized so that the combustiblesubstance, once reduced in size by burning, can fall through the outletunder the action of gravity onto the sample holder. Alternatively oradditionally pressure which is generated by the burning substance exertsa force on the substance which, at least initially, propels thesubstance towards the sample holder.

[0013] The invention also provides a method of igniting a sample in acalorimeter which includes the steps of igniting a combustible substanceand allowing the burning substance to move into contact with a sampleinside the calorimeter thereby to ignite the sample.

[0014] Although the combustible substance may be allowed, or caused, tomove in any appropriate way inside the calorimeter, it is preferred thatthe combustible substance moves under gravity action, ie. falls, or ispropelled at least initially by pressure generated by the burningsubstance, into contact with the sample.

[0015] The combustible substance may be liquid or solid. If liquid thecombustible substance may be a drop of the liquid which is placed in anyappropriate way, for example by injection means in the calorimeter at alocation at which it is in contact with, or in proximity to, a suitableheating device.

[0016] If the combustible substance is solid then preferably the solidis provided in a granular or pelletised form.

[0017] Preferably the combustible substance is caused to ignite bymaking use of electrical heating means

[0018] It is important that the combustible substance burns relativelyslowly even inside the highly oxygen charged atmosphere which prevailsin a calorimeter. Ignition of the combustible substance takes place at apoint which is spaced from the sample in the calorimeter and the burningsubstance, while burning, moves or is caused to move to the samplematerial so that it reaches the sample while still burning. Thecombustible substance must therefore burn for a period which isrelatively long at least compared to the combustion period of thread orcotton which is conventionally used for igniting a calorimetric sample.

[0019] The invention also extends to a combustible substance for use inthe apparatus or method of the invention. The combustible substance maybe liquid or solid.

[0020] In the former instance the combustible liquid may be formed froma mixture of at least two components such as water and alcohol. Theratio of water to alcohol is adjusted according to the particularcircumstances in the calorimeter, and the drop size of the liquid, toensure that a falling liquid drop is not fully consumed by the ignitionprocess before the drop impacts on the sample.

[0021] If the combustible substance is solid then it is preferablyprovided in granular or pelletised form A suitable substance is forexample a mixture of benzoic acid and alumina powder.

[0022] The invention is however not limited in the nature or type ofcombustible substance which can be used provided only that thecombustible substance, once ignited, will burn for a period which issufficiently long to ensure that the burning substance impacts thesample in the calorimeter

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention is further described by way of examples withreference to the accompanying drawings in which:

[0024]FIG. 1 is a schematic side view of a calorimeter wherein a sampleis ignited in accordance with the principles of the invention, and

[0025]FIGS. 2 and 3 illustrate possible variations of the apparatus ofthe invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0026]FIG. 1 of the accompanying drawings illustrates, somewhatschematically and from the side, a portion of a calorimeter 10 wherein asample is ignited in accordance with the principles of the invention.

[0027]FIG. 1 schematically depicts only that part of a calorimeter bombwhich is necessary for an understanding of the invention. Generally thebomb is constructed in a conventional manner and, for this reason, isonly shown notionally by means of dotted lines 12 and not furtherdescribed herein. The calorimeter includes a removable lid 14. Oxygenfrom a suitable source 16 can be charged into the interior of the bomb.A conventional electronic control system, schematically represented by ablock 18, which includes temperature sensors and the like, is providedfor operating, and monitoring the operation of, the bomb. Again nonovelty is claimed in respect of these components and, for this reason,as is the case of the oxygen charging system, no further description isincluded in this specification.

[0028] Inside the bomb and supported in any appropriate manner or bystructure of the bomb, are two spaced support members 20 and 22respectively. These members are for example made from a heat resistingmaterial such as stainless steel and include internal electricalconductors, indicated schematically by dotted lines 19, which lead fromthe electronic system 18 to electrodes 24 and 26 which extend towardsone another from the respective members 20 and 22.

[0029] A funnel-shaped holder 28, which is made from a suitable heatresisting material, is supported by the electrodes at a central positioninside the bomb. A mouth 30 of the funnel faces upwardly and a dischargespout 32 of the funnel faces downwardly and is directly positioned overa crucible 34 which is of known construction and which is suitablysupported The crucible, in use of the calorimeter, receives a sample 36of material which is to be tested.

[0030] As has been indicated in the preamble of this specification manycalorimeters have been developed to the point at which they aresubstantially completely automated in operation. Thus the placing of asample in the crucible, the closure of the bomb, the charging of thebomb with oxygen, the ignition of the sample and the monitoring of thesubsequent reactions, and any other steps save for preliminary workrequired to ignite the sample, can all be automated and carried outautomatically in the correct sequence.

[0031] A filament wire 38 of a relatively robust construction ispositioned inside the conical holder 28 so that it traverses the outlet32, effectively reducing the cross sectional area of the outlet, and isconnected to and between the electrodes 24 and 26.

[0032] A dispensing device 40 is positioned outside the bomb at anyappropriate location which depends, at least, on the nature of thedispensing device. Any appropriate dispensing device can be used. Inthis instance a housing of the dispensing device includes a door 42which is movable by means of an actuator 44 under the control of theelectronic unit 18. The door 42 is movable between a first position atwhich it exposes an opening 46 in the housing of the dispenser and asecond position at which the opening is totally sealed. The arrangementis such that the door, when moved by the actuator, is opened and thenclosed thereby to allow one pellet 48, from a plurality of pellets inthe housing of the device 40, to be discharged through the opening. Thepellet then falls under gravity action and is guided inside a chute 50thereby to fall directly into the funnel-shaped holder 28. The door isdesigned so that when it closes the opening 46 it simultaneouslyeffectively seals the opening in a gas-tight manner which is well ableto withstand the working requirements of the calorimeter.

[0033] In this example of the invention each pellet 48 is made to apredetermined size from suitable ingredients. For example the pelletsmay be formed from a precisely formed mixture of benzoic acid andalumina powder which is pelletised and which is then formed into aplurality of pellets, each pellet being of an exact size eg.approximately 0.5 mm in diameter, and hence of an exact weight. Thepellets should be as small as possible to limit extraneous effectsproduced in the bomb by the ignition of the pellets.

[0034] As has been noted the dispenser 40 causes one of the pellets 48to be passed through the opening 46 into the holder 28. The importantaspect about this step is that it can be carried out totallyautomatically. In a preferred form of the invention all of the remainingsteps in the calorimetric process are also carried out automatically.Thus the sample 36 is placed in the crucible 34 and the bomb is closedand charged with oxygen The electronic unit then applies a voltage tothe electrodes 24 and 26 which causes a current of a predeterminedmagnitude to flow through the filament wire 38 for a predeterminedperiod. The pellet 48 which is in the holder initially rests on thefilament wire 38. The filament wire, when heated to the required extent,caused the pellet 48 to be ignited. The pellet commences burning,although it burns relatively slowly due to its composition andstructure. Ultimately however the pellet is reduced in size sufficientlyso that it can fall under gravity action past the filament 38 andthrough the outlet spout 32. The pellet continues burning as it fallsthrough the oxygen in the bomb onto the sample in the crucible. Theburning pellet, when it impacts the sample, almost instantaneouslycauses ignition of the sample so that the calorimetric measuring processcan be completed.

[0035] The crux of the invention is that the combustible substanceconstituted by the pellet is ignited and the pellet is then caused orallowed to migrate, while burning, by gravity or other action, onto ornear the sample material under test in the calorimeter thereby causingthe sample material to ignited.

[0036] The aforementioned principle can be used in other ways to causeignition of the sample material FIGS. 2 and 3, illustrate, somewhatconceptually, two variations of the invention. In the former instance afilament wire 60 is bent with a central loop 62 and is supported betweenextremities of spaced members 20A and 22A which are similar to themembers 20 and 22 respectively in FIG. 1. A dispenser places acombustible substance 64 on the loop The combustible substance could bea pellet of the type described in connection with FIG. 1 Alternativelyit could be a drop of a combustible liquid such as a mixture of alcoholand water which is made to a suitable ratio of ingredients and which isthen placed, for example by means of a drop injection mechanism 66, ofany appropriate construction, directly onto the loop 62. The mechanism66 is of a type known in the art, and no novelty is claimed in respectthereof. When activated it produces a single droplet of the combustibleliquid mixture which is directed onto the loop 62. The liquid adheres,due to capillary action or surface tension effects, to the loop 62. Whenthe filament wire is heated by passing a current through the wire theloop 62 heats the liquid drop which adheres to the loop and the drop isignited and burns, again relatively slowly, until its size is reduced tosuch an extent that the drops falls through the loop under gravityaction directly onto a sample 68 contained in an underlying crucible 70.The sample is thereby ignited.

[0037] The combustible drop 64 is sufficiently small eg. again of theorder of 0.5 mm in diameter, a size which is similar to the diameter ofthe loop 62, to ensure that initially the drop adheres to the loop. Alsothe amount of energy released into the bomb by ignition of the drop issmall.

[0038] In the arrangement shown in FIG. 3 like reference numeralsdesignate like components. The filament wire 60 is not bent to form aloop but instead directly traverses a space between walls of a holder 72which is supported by the members 20A and 20B. A combustible drop 74, egof water and alcohol, is introduced into the interior of a housing ofthe holder through an inlet or upper opening 76 and comes to rest onlower inner surfaces of the holder adjacent an outlet 78 from theholder. When the filament wire is heated by the application of anelectric current the drop is ignited and once it has burnt to someextent the pressure which is built up inside the holder by thiscombustion causes the remainder of the drop to be ejected through theoutlet 78 onto a sample 68 in an underlying crucible 70 Again it is tobe noted, with FIGS. 2 and 3, that the invention makes use of a separatesubstance which is ignited and, while burning, is allowed to movethrough the interior of the bomb into contact with the sample materialwhich is then caused to ignite.

[0039] Clearly the principles of the invention can be used in ways otherthan those described in connection with FIGS. 1 to 3 and such variationsare intended to fall within the scope of the present invention.

1. Apparatus for igniting a sample in a calorimeter which includes aheating device, holder means for placing a combustible substance incontact with or in proximity to the heating device thereby to ignite thesubstance which, once burnt to a predetermined extent, is movable awayfrom the heating device, and a sample holder which is positioned toreceive the burning substance as it moves away from the heating device.2. Apparatus according to claim 1 wherein the heating device is heatedby the passage of electric current at least to a temperature which isequal to the ignition temperature of the substance.
 3. Apparatusaccording to claim 1 or 2 wherein the heating device includes at leastone filament wire shaped to receive the combustible substance. 4.Apparatus according to claim 1 or 2 wherein the holder means is afunnel-shaped component in which the combustible substance is locatedand the heating device is positioned inside the funnel so that thecombustible sample, inside the funnel, is automatically brought intocontact with, or in proximity to, the heating device.
 5. Apparatusaccording to claim 4 wherein the funnel includes an outlet which islocated above the sample holder with the outlet being sized so that thecombustible substance, once reduced in size by burning, can fall throughthe outlet under the action of gravity onto the sample holder. 6.Apparatus according to claim 1 or 2 wherein the holder includes ahousing with an inlet through which the combustible substance isintroduced into an interior of the housing, and an outlet through whichthe burning combustible substance is ejected after ignition by the saidheating device.
 7. A method of igniting a sample in a calorimeter whichincludes the steps of igniting a combustible substance and allowing theburning substance to move into contact with a sample inside thecalorimeter thereby to ignite the sample.
 8. A method according to claim7 wherein the combustible substance moves under gravity action or ispropelled at least initially by pressure generated by the burningsubstance, into contact with the sample.
 9. A method according to claim7 or 8 wherein the combustible substance is a liquid drop.
 10. A methodaccording to claim 7 or 8 wherein the combustible substance is a solidin a granular or pelletised form.
 11. A method according to any one ofclaims 7 to 10 wherein the combustible substance is caused to ignite bymaking use of electrical heating means.
 12. A combustible substance foruse in the apparatus of any one of claims 1 to 6 which comprises agranular or pelletised mixture of benzoic acid and alumina powder.